Networks are expected to have high reliability when communication is conducted over multiple networks. To improve network reliability, networks preferably have a physical redundant route between various information transmission devices based on bridges that represent one type of device for relaying data in networks. A ring topology is one type of network configuration having redundancy.
A network having a ring topology connects nodes on the network in a ring shape. Herein-below, a network with a ring topology is simply referred to as a “ring.” It is conceivable that frames with unknown addresses may loop in the ring making normal communication difficult. Accordingly, relaying of a frame from a specific port is interrupted using a protocol for ring control and a frame relay path between any of the network devices is uniquely decided. The point where this interruption occurs may be called a “block point” and a technique for interrupting the network and resolving the looping is called “blocking.” When a failure occurs in a network, a ring that uses this type of blocking is able to restart communication in a path in which the failure did not occur by changing the block point.
Recently, communication using virtual local area networks (VLANs) has increased in order to more effectively use network resources. A VLAN is a virtual network using a VLAN identification (VLAN ID) as an identifier. A VLAN ID is defined in the Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.1Q, and is an ID for using one physical network as a plurality of virtual networks. A VLAN ID is stored in a VLAN tag field inside a frame and one VLAN ID corresponds to one network. VLAN setting is generally conducted for conducting communication in a network using a ring topology.
Japanese Patent Laid-open No. 2006-261806 discusses a technique, which is known as a conventional technique in a network having a ring topology, for setting a block point in each VLAN and selecting a VLAN having the path with the fewest number of hops as the optimal path.